1. Field of the Invention
The present invention relates generally to a wind turbine, and more specifically to a large floating vertical axis wind turbine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Wind turbines are used to generate electrical energy from wind. Wind turbines can be horizontal axis wind turbines or vertical axis wind turbines (also referred to as Darrieus turbines). The horizontal axis wind turbines are the most common of the two types and typically include three blades extending out from a central hub and looks like a giant propeller blade. Wind turbines are mostly used on land, but are starting to be used offshore in deep water because that is where strong and sustainable wind is found.
Giant horizontal axis wind turbines have been built in the range of up to 5 MWatts in power. However, the most common size is in the 1 to 2 MW size. Use of the smaller horizontal axis wind turbines is preferred because they last longer than the larger ones. The larger the turbine, the heavier the weight of the blades. Horizontal axis wind turbines require bearings to rotatably support the very heavy turbine blades. The bearings cannot handle the heavy loads from these larger turbines and thus fail often.
Another design problem with horizontal axis wind turbines is the gear box. A gear box is required to step up the rotational speed from the slow blade hub shaft to the shaft of the generator. The gear box is what typically fails first in these horizontal axis wind turbines. The gear box is also located in the nacelle, which is located on top of a tall tower that can be 300 feet in height. The nacelle is the enclosed unit in which all the contents of the electrical energy generating equipment is located. These important parts of the turbine are therefore located in difficult to reach location.
Wind turbines are being considered for use off shore because of the strong winds available. Currently, a typical horizontal axis wind turbine is being placed on a tall floating cylinder that is anchored to the sea bed by cables. Most of the cylinder floats below the water surface with the wind turbine mounted on the top surface and operating just like those located on land. These offshore wind turbines also suffer from the same problems discussed above.
One prior art wind turbine that solved the problem with the bearings is U.S. Pat. No. 7,397,144 issued to Brostmeyer et al on Jul. 8, 2008 and entitled BEARING-LESS FLOATING WIND TURBINE and in which the applicant's of the present invention are also inventors of this patent. Instead of supporting the turbine blades by bearings, the Brostmeyer patent uses a giant doughnut shaped floating barge on which the blades are fixed to rotate along with. Thus, the blades rotate along with the floating barge. With this design, the blades can be as large as structurally possible without any concern for bearings. One problem since discovered by the inventors has been the large surface area of the floating barge that is exposed to the water. A large viscous force would be formed as the floating barge rotates within the body of water. This large viscous force would have to be overcome by any torque developed by the wind reacting on the vertical axis blades.
In an attempt to overcome the problems described above and with the Brostmeyer patent above, the applicant's developed the next generation bearingless floating wind turbine that is described in U.S. Pat. No. 7,750,492 issued to Ryznic et al. on Jul. 6, 2010 and entitled BEARINGLESS FLOATING WIND TURBINE. This design uses a floating support that has a long narrow neck with a larger diameter bulb section on the bottom end and a larger diameter section on the top end. Because of the narrow neck section, the surface area for exposure to the water is significantly reduced over that of the first generation bearingless floating wind turbine with the doughnut shaped floating barge. The larger diameter bulb section on the bottom is filled with a ballast material and thus lowers the center of gravity of the floating wind turbine below the center of buoyancy. In this design, the blades are vertical axis turbine blades or Darrieus type blades.
Another benefit to the second generation bearingless floating wind turbine is that a large diameter permanent magnet electric generator can be used instead of the prior art generators that require a gear box. These permanent magnet generators are direct drive generators and therefore do not use a gear box. These direct drive generators are not used in the vertical axis wind turbines because they cannot be integrated in the small space and at the great heights that sit on top of the tall towers. Because the second generation bearingless floating wind turbine uses a floating cylinder with a large diameter space on top, a large diameter vertical axis permanence magnet direct drive generator can be used. The applicant's have since discovered that this second generation floating vertical axis wind turbine tends to tilt to one side during operation because of the lack of upper buoyancy support for the tall and narrow neck section.